1. Field of the Invention
The present invention relates to an industrial robot with a telescopic horizontal arm, and more particularly, to a cylindrical coordinate type industrial robot provided with an upright column extending from a lower turnable base and having a vertical axis, and a horizontal arm mounted on the upright column to be telescopically movable in a horizontal axis perpendicular to the vertical axis of the upright column and having an improved drive source for a telescopic movement of the horizontal arm.
2. Description of the Related Art
In various conventional industrial robots, a cylindrical coordinate type industrial robot is provided with a horizontal arm telescopically movable in a horizontal axis. FIG. 5 illustrates a conventional horizontal arm of the cylindrical coordinate type industrial robot. In FIG. 5, the horizontal arm unit is mounted on a vertically intermediate portion of a vertical column 3 via arm casing 2 having one end on which a drive motor M.sub.1 is fixedly mounted, and provided with a ball screw shaft 4 arranged to be axially horizontally extended in the arm casing 2 and rotatively driven by the drive motor M.sub.1 via a belt-pulley transmission unit 5 employing a timing belt. The horizontal arm is further provided with a ball screw nut 6 which is threadedly engaged with the ball screw shaft 4 to be moved along the axis of the ball screw shaft 4, and is connected, via a connecting member 10, to a telescopic arm 8 arranged to be in parallel with the ball screw shaft 4 and moved together with the ball screw nut 6 in an axial direction corresponding to a horizontal telescopic axis of the horizontal arm unit. Namely when the ball screw shaft 4 is rotatively driven by the drive motor M.sub.1, the ball screw nut 6 is linearly axially moved along the axis of the ball screw shaft 4 due to a rotation to linear movement converting action of these threadedly engaged elements. The linear movement of the ball screw nut 6 causes the movement of the telescopic arm 8 via the connecting member 10 in the horizontal telescopic axis of the horizontal arm unit. The telescopic arm 8 has one external end thereof to which a robot wrist member is attached.
Japanese Unexamined (Kokai) Patent Publication No. 60-123294 discloses a different construction of a conventional telescopic horizontal arm provided with two first arms and two second arms, which are moved by the two separate assemblies of ball screw shafts and nuts.
In the former conventional horizontal arm unit of the cylindrical coordinate type industrial robot shown in FIG. 5, the maximum amount of telescopic movement of the telescopic arm 8 from a retracted position wherein the telescopic arm 8 is fully retracted into the arm casing 2 to an extended position wherein the telescopic arm 8 is fully extended from the arm casing 2 is determined only by the length of the telescopic arm 8 per se, as illustrated in FIG. 4. Therefore, when the maximum amount "L" of telescopic movement of the telescopic arm 8 is large, the length of the telescopic arm 8 and the arm casing 2 must be accordingly long, and therefore, the arm housing 2 supported by the upright column 3 must have a long portion extended in a rearward direction, i.e., in a direction opposite to the direction in which the telescopic arm 8 is extended from the retracted position. As a result, when the cylindrical coordinate industrial robot is turned about a vertical axis, the long rearward portion of the arm casing 2 of the horizontal arm unit sweeps over a wide circular area having a radius R.sub.1 and designated by hatching lines in FIG. 4. Therefore, the wide circular area of which the radius is "R.sub.1 " becomes an area which must be always left unoccupied, to enable a free turning of the horizontal arm unit about the vertical axis without obstruction. Thus, when the conventional cylindrical coordinate type industrial robot having a horizontal telescopic arm is located at a site for use in a working area, the wide circular unoccupied area must be allowed around the robot, for a free motion of the robot, and accordingly, an effective use of the working area is prevented.
In the latter conventional industrial robot with a horizontal telescopic arm unit disclosed in Japanese Unexamined Patent Publication No. 60-123294, the first and second assembly of two arms are accommodated in a single boom, to be smoothly horizontally moved by the drive motor and the ball screw and nut assemblies housed in the boom via two bearing units. Therefore, the horizontal telescopic arm unit becomes considerably heavy, and the drive motor for the telescopic arm unit must have a large output power. Further, when the construction of the horizontal arm unit of the Japanese Unexamined Patent Publication No. 60-123294 is adopted as a horizontal arm of a cylindrical coordinate type industrial robot, drive motors for vertical motion of the horizontal arm unit on a vertical column and for a turning motion of the same arm about a vertical axis via a turnable body must bear a heavy load, respectively, during the operation.